1. Field of the Invention
This invention relates to a coating device and a coating method using an extrusion die, and particularly to a coating device and a coating method which are effective for high-speed coating with an organic solvent.
2. Description of the Related Art
Curtain coating has been known as a method of coating a polyethylene terephthalate film or a paper support with a non-magnetic paint, a solvent or water in a non-contact manner.
This coating method is adapted for causing a coating solution extruded from a die to drop by its tare weight so as to form and apply a coating film onto a support. Therefore, the flowing speed of the coating solution is low, and as high-speed coating is to be carried out, the coating solution is broken by an air film accompanying the support which travels at a high speed, or the air enters a contact surface between the support and the coating solution, thus generating uneven coating and deterioration in coating quality. With respect to a magnetic tape in particular, since a polyethylene terephthalate or polyethylene naphthalate film having a mirror surface is used, the air film is likely to be generated and therefore high-speed coating is technically difficult.
The curtain coating method does not enable high-speed coating for the following reasons. That is, since the flowing speed of the coating solution is limited to a low speed by the gravity due to drop by its tare weight, the rigidity of the coating solution film is low. Also, the coating solution film cannot endure the wind pressure of the air film accompanying the flexible support traveling in the traverse direction of the coating film, or the air enters between the coating solution film and the support.
According to the known information, patented inventions are reported such that a preventive measure against the air film is taken by providing a reduced-pressure chamber at the entrance of a coating portion or such that a preparatory chamber is filled with a gas which is likely to be absorbed in the coating solution. However, no significant increase in speed can be expected and devices therefor are complicated and more difficult to operate.